Current millimeter wave imaging arrays mostly use convex lenses to focus an image onto a flat focal plane. The angular field of view is then limited to the amount of defocusing that can be tolerated away from the center of the focal plane. The presently disclosed technology shows how to practically assemble multiple focal planes around a spherical lens for a very wide angular field of view. In addition, the presently disclosed technology teaches how to use monolithically integrated diode and antenna detector chips that may be flip-chip attached to a folded hybrid printed circuit board to create a compact, three-dimensional imaging system with a wide field of view.
The millimeter wave imaging assembly described herein may be used in many different possible applications, including vehicle collision avoidance system for use in harsh weather (such as fog), wide angle imaging for aircraft landing systems, and battlefield and civil disaster imaging through clouds and smoke. Millimeter wave imaging is an aid to infrared and/or visible imaging systems when harsh environmental conditions obscure the shorter wavelength systems.
The prior art includes:
B. Schoenlinner, X. Wu, J. P. Ebling, G. V. Eleftheriades, and G. M. Rebiez, “Wide-Scan Spherical Lens Antennas for Automotive Radars,” IEEE Trans. Microwave Theory Technique, Vol. 50, No. 9, September 2002, pp. 2166-2175,
This paper describes a millimeter wave automotive radar that uses a spherical lens and an array of pick-up antennas that surround the lens. This system uses a spherical lens for focusing and printed circuit tapered slot antennas to receive the signal and channel it into a detector. The antenna array surrounds the lens in one diametric plane only, thus it would have to be physically scanned to receive signals from other planes and thus form an image. The presently disclosed technology utilizes a dielectric resonator antenna fabricated monolithically from the same substrate that has the detector diode. This allows a much denser fill of pixels and also allows us to produce an image from multiple diametric planes simultaneously.
J. H. Schaffner, J. J. Lynch, and D. F. Sievenpiper, “Antenna System and RF Signal Interference Abatement Method,” Patent Application Publication US2003/0043086 A1, Mar. 6, 2003.
This published patent application includes a description of using a spherical lens surrounded by patch antenna elements to simultaneously focus on multiple GPS satellites over a very wide field of view. The major differences between that patent application and the present disclosure are:
The prior art does not need dense angular discrimination since the locations of the GPS satellites are frequently widely spread across the celestial field of view. The present disclosure shows how to densely pack detectors for a much finer angular resolution that is needed for imaging systems.
The prior art assumes that the antennas to which the signals are focused are separate from the lens and in fact stand off from the lens. In this disclosure we describe a single imaging system and method of assembly whereby the focal plane arrays are in intimate contact with the lens to form a very compact system.
B. Tomasic, J. Turtle, and S. Liu, “A geodesic sphere phased array antenna for satellite control and communications,” presented at the URSI General Assembly 2002 Conference, Jul. 15, 2002, paper B8.0.9.
This paper describes the use of a geodesic dome to support a phased array antenna for wide field of view radar scanning. The difference between this report and the present disclosure is that the report describes a phased array antenna while we describe an imaging array. In the paper, the antenna elements radiate away from the spherical surface and each facet of the dome is fed through a corporate feed network. This disclosure is not directed to a phased array antenna, but rather relies on a dielectric lens to focus the point of an image.
Additional prior art documents include:    1. H. Schrank and J. Sanford, “A Luneburg Lens Update,” IEEE Antennas and Propagation Magazine, Vol. 37, No. 1, February 1995, pp. 76-79.    2. G. Bekefi and G. W. Farnell, “A Homogeneous Dielectric Sphere as a Microwave Lens,” Canadian Journal of Physics, Vol. 34, 1956, pp. 790-803.    3. R. P Hsia, S. Cheng, W. R Geck., C. W Domier. N. C., Luhmann, Jr.; “Millimeter-wave Schottky diode imaging array development,” Microwave Conference Proceedings, 1993. APMC '93., 1993 Asia-Pacific, Vol. 1, 1993, pp. 9-12.    4. J. N. Schulman, D. H. Chow, C. W. Pobanz, H. L. Dunlap, and C. D. Haeussler, “Sb-heterostructure millimeter wave zero-bias diodes,” Device Research Conference 2000, Conference Digest, 58th DRC, Jun. 19-21, 2000, pp. 57-58.    5. Yongxi, S. Iwata, and E. Yamashita, “Optimal design of an offset-fed, twin-slot antenna element for millimeter-wave imaging arrays,” Microwave and Guided Wave Letters, Vol. 4, No. 7, July 1994, pp. 232-234.    6. K. Uehara, K. Miyashita, K.-I. Nasume, K. Hatakeyama, and K. Mizuno, “Lens-coupled imaging arrays for the millimeter- and submillimter-wave regions,” IEEE Trans. Microwave Theory Technique, Vol. 40, No. 5, May 1992, pp. 806-811.    7. Eugene Hecht, Optics, Addison-Wesley Publishing Company, Reading, Mass., 1988, pg. 422.    8. R. Buckminster Fuller, “Building Construction,” U.S. Pat. No. 2,682,235, June 1954.    9. W. H. Haydl, J. Braunstein, T. Kitazawa, M. Schlechtweg, P. Tasker, and L. F. Eastman, “Attenuation of Millimeter Wave Coplanar Lines on Gallium Arsenide and Indium Phosphide over the Range 1-60 GHz,” Digest of the 1992 IEEE MTT-S International Symposium, 1992, pp. 349-352.    10. M. S. Al Saameh, Y. M. M Antar, and G. Seguin, “Coplanar-Waveguide-Fed Slot-Coupled Rectangular Dielectric Resonator Antenna,” IEEE Trans. Antenna Propag.,” Vol. 50, No. 10, October 2002, pp. 1415-1419.    11. H. Morishita, K. Hirasawa, and K. Fujimoto, “Analysis of a Cavity-Backed Annular Slot Antenna with One Point Shorted,” IEEE Trans. Antenna Propag,” Vol. 39, No. 10, October 2001, pp. 1472-1478.    12. J. N. Schulman, V. Kolinko, M. Morgan, C. Martin, S. Clark, J. Lovberg, S. Thomas III, J. Zinck, and Y. K. Boegeman, “W-Band Direct Detection Circuit Performance with Sb-Heterostructure Diodes,” Submitted for publication to IEEE Microwave and Wireless Components Letters, October 2003.